Parcells is a franchise builder. He left Belichick in New England with the core (Brown, Bruschi, McGinest, etc.) that went on to win those titles.
He hired coaches like Payton, Coughlin, and Belichick, and he salvaged 4 miserable franchises from the depths of their divisions.
Lotta his haters also don't realize that Belichick was some LB coach when Parcells turned the Giants from a 3-12 team into a playoff contender two years in a row before their Super Bowl titles. Parcells was savvy enough to promote Belichick to the D. coordinator job, but he built the team, and got them into the playoffs before Belichick was even in a prominent role on his staff.
Even Jerry Jones knew that Parcells would be the man to turn the franchise around and get him support for a new stadium. And that's exactly what happened here. Dallas has been relevant for about a decade thanks to him. It took Garrett 5 years to ruin what we had going here. Just proves how solid the team was for a bit there.